The visual system adjusts to stabilize object color appearance against changes in illumination. This proposal consist of experiments designed to study the adjustments, which is often called color consistency. Understanding color consistency is necessary for a complete theory of human color vision. In addition, color consistency is an example of a larger class of perceptual constancies (e.g. size consistency and shape consistency) that together allow us to perceive a stable physical world. As such, a detailed characterization of the color system may provide insights that generalize to these other perceptual systems. The first set of experiments is designed to develop computer display technology for studying color constancy. The experiments will compare performance for natural viewing with that for a variety of display conditions. By titrating the richness of the displays, we will determine what factors are important for color constancy and how well they can be stimulated. The second set of experiments will exploit the display technology to characterize human color constancy. Particular emphasis will be placed on determining how well the visual system can separate illuminant and object spectra and on relating human performance to computational models.